The object of this research is to determine the three dimensional structure of proteins and nucleic acids with special reference to the manner in which they interact with each other. The method which is used is that of crystal x-ray diffraction studies of the macromolecular proteins, nucleic acids or their complexes. The systems which are currently under investigation include study of the structure of yeast aminoacyl and peptidyl tRNA Phe, the structure of E. coli tRNA Met which initiates the synthesis of proteins, the structure of a DNA binding protein, gene 5 protein, and a complex of gene 5 DNA binding protein with oligonucleotides. We are also studying the structure of the E. coli elongation factor EF-Tu which normally binds to aminoacyl tRNA. In addition, the structure of self-complementary oligodeoxynucleotides is being studied such as deoxy CGCG, deoxy GCGC as well as its interaction with intercalator molecules.